The present invention relates to a cutting tool insert for machining by chip removal and wear resistant coating comprising at least one (Zr,Al)N layer with a low Zr content grown by physical vapour deposition (PVD) and preferably by cathodic are evaporation or magnetron sputtering. This insert is particularly useful in metal cutting applications generating high temperatures, e.g., machining of steel, stainless steel and hardened steel.
TiN-layers have been widely used for surface protective applications. In order to improve the oxidation resistance of these layers, work began in the mid-1980's with adding aluminum to TiN. The compound thus formed, cubic-phase (TixAl1-x)N, was found to have superior oxidation resistance and enabled greater cutting speeds during machining, prolonged tool life, machining of harder materials, and improved manufacturing economy. Improved coating performance in metal cutting applications has been obtained by precipitation hardening of (TixAl1-x)N and also disclosed in U.S. Pat. No. 7,083,868 and U.S. Pat. No. 7,056,602.
Zr1-XAlXN (0≦x≦1.0) layers have been synthesized by the cathodic are evaporation using alloyed and/or metal cathodes, H. Hasegawa et al, Surf. Coat. Tech. 200 (2005). The peaks of Zr1-XAlXN (x=0.37) showed a NaCl structure that changed to a wurtzite structure at x=0.50.
EP 1 785 504 discloses a surface-coated base material and a high hardness coating formed on or over said base material. Said high hardness coating comprises a coating layer containing a nitride compound with Al as main component and at least one element selected from the group consisting of Zr, Hf, Pd, Jr and the rare earth elements.
US 2002/0166606 discloses a method of coating a metal substrate by a metal compound coating comprising TiN, TiCN, AlTiN, TiAlN, ZrN, ZrCN, AlZrCN, or AlZrTiN using a vacuum chamber process such as physical vapor deposition (PVD) or chemical vapor deposition (CVD).
The trends towards dry-work processes for environmental protection, i.e., metal cutting operation without using cutting fluids (lubricants) and accelerated machining speed with improved process put even higher demands on the characteristics of the tool materials due to an increased tool cutting-edge temperature. In particular, coating stability at high temperatures, e.g., oxidation- and wear-resistance, has become even more crucial.
It is an object of the present invention to provide a coated cutting tool insert with improved performance in metal cutting applications at elevated temperatures.
Surprisingly, a low Zr content in (Zr,Al)N layers deposited on cutting tools inserts significantly improves their high temperature performance and edge integrity during metal cutting.